The specific aims of this project are to firm up assignments of conformationally sensitive lipid ester vibrational modes; to extend Raman studies of the effect of hydration, cation binding, and pH on the temperature phase changes and the head group and acyl conformations of lipids to include sphingomyelin, phsophatidyl-inositol, and phosphatidylglycerol; to determine whether biologically significant packing changes (such as anomalous mid-transition acyl region changes and hex II phases) occur in mixed lipid systems and what factors may contribute to inducing these to occur; to determine specific head group conformation and interaction requirements which contribute to the activity of biologically active phospholipids by studying platelet activating factor and structural analogues. The techniques to be chiefly used for these investigations are Raman spectroscopy and infrared spectroscopy. Conformationally sensitive vibrational modes will be used to determine conformation and interactions. Conformation and interactions at the surfaces of phospholipid aggregates are to be related to membrane-mediated events and membrane properties.